1. Field of the Invention
The present invention relates to a device suitable for a laser-type bar code reader which is used in a POS (point of sales) system in the distribution industry, and more particularly, to a laser lighting control device in a laser scanning device which reads a bar code or the like using a reflected laser beam.
2. Description of the Related Art
FIG. 5 is a block diagram showing the configuration of a bar code reading device (bar code reader). Referring now to FIG. 5, numeral 1 represents a bar code printed on the surface of an article, the bar code being formed of plural black bars and white bars arranged alternatively. A predetermined datum is represented based on the width of each black bar and the width of each white bar.
An optical system (laser scanning device) 2 irradiates a laser beam L2 to the bar code 1 and receives a reflected light R1, or the laser beam L2 reflected by the bar code 1. The optical system 2 also comprises a laser emitting unit 3, a scanning mechanism 4 and an optical converter unit 5. The laser emitting unit 3 includes a semiconductor laser device for emitting the laser beam L1. The scanning mechanism 4 comprises a polygon mirror that is rotatably driven with, for example, a motor. The scanning mechanism 4 also irradiates the laser beam L2 to the plural black bars and white bars forming the bar code 1, the beam L2 formed by reflecting the laser beam L1 from the laser emitting unit 3, while it moves and scans it at a fixed rate in the direction perpendicular to the black and white bars of the bar code 1.
The scanning mechanism 4 irradiates the reflected beam R1 as the reflected beam R2 to the photoelectric converter unit 5, the reflected beam R1 being the laser beam L2 reflected by the bar code 1 and traveled with the laser beam L2 scanned.
The photoelectric converter unit 5 is formed of a photoelectric converting element, for example, a photo diode. The photoelectric converter unit 5 receives the reflected light R2 (light input signal) via the scanning mechanism 4 to convert it to an electric signal (analog value) corresponding to the light amount thereof.
In FIG. 5, the A/D converter unit 6 digitizes the electric signal from the photoelectric converter unit 5 to convert it to a binary signal including a black level signal corresponding to each black portion and a white level signal corresponding to each white portion in the bar code 1. The white level signal represents a high level signal and the black level signal represents a low level signal because the light amount of the light R2 reflected by each white bar is larger than that of the light R2 reflected by each black bar in the binary signal.
The bar width counter 7 counts the clock signal from the clock generator 8. The bar width counter 7 also outputs as a clock signal count value the time widths of the black level signal portion and the white level signal portion of a binary signal from the A/D converter unit 6, or each black bar width and each white bar width of an actual bar code 1.
Furthermore, the memory 9 stores the bar width count value from the bar width counter 7. The CPU 10 extracts and demodulates predetermined data of the bar code 1 based on the bar width count value (a value corresponding to each black bar width or each white bar width) stored in the memory 9.
In the above structure, the scanning mechanism 4 irradiates the laser beam L1 emitted from the laser emitting unit 3 as the laser beam L2 to the black bars and the white bars of the bar code 1 while it moves and scans it at a constant rate in the direction perpendicular to the black bars and white bars of the bar code 1.
The laser beam L2 emitted from the scanning mechanism 4 is scatteringly reflected on a portion of the bar code 1 and is re-irradiated as the reflected light R1 to the scanning mechanism 4. The reflected light R1 varies its reflection angle as the laser beam L2 scans and moves. However, the polygon mirror comprising the scanning mechanism 4 reflects the reflected light R1 as the reflected light R2 to the photoelectric element in the photoelectric converter unit 5 arranged at a predetermined place.
The photoelectric converter unit 5 converts the reflected light R2 to an electric signal corresponding to the amount thereof. The A/D converter unit 6 digitalizes the electric signal into a binary signal including a black level signal corresponding to each black portion of the bar code 1 and a white level signal corresponding to each white portion of the bar code 1.
Then, the bar width counter 7 counts the clock signal from the clock generator 8 to measure as a clock signal count value the time width (values corresponding to the widths of each black portion and each white portion in an actual bar code 1) of the black level signal portion and a white level signal portion of a binary signal from the A/D converter unit 6. The memory 9 temporarily stores the count value. The CPU 10 subjects the bar width count value stored in the memory 9 to a predetermined demodulation process to extract and demodulate the determined data of the bar code 1.
Generally, the laser scanning device (optical system) 2 includes a laser diode (semiconductor laser) as the light source of the laser emitting unit 3 to realize a miniaturized device and a power source with small power consumption.
In order to prolong the operational life of the laser diode, a Gun-type laser scanner device with a trigger switch and a laser scanner device with an item sensor are used.
The Gun-type laser scanning device emits the laser beam by performing a lighting control of the laser light source only when a trigger switch is turned on. The laser scanning device with an item sensor subjects the laser light source to a lighting control only when the item sensor detects the fact that the object with a bar code to be read is close to the device, whereby a laser beam is emitted.
The laser scanning device subjects the laser light source to a lighting drive only when reading a bar code or the like is needed so that the serviceable life of the laser light source such as a laser diode is prolonged.
As described above, in order to prolong the operational life of the laser scanning device, the device with a laser light source has been desired to prolong further the operational life of the laser light source. In order to solve the problem, it is needed to execute a certain life control of the laser light source.
In order to judge whether there is a variation in quality of the laser light source or the laser light source has been fully used up to its substantial use limit (life), the laser light source must be taken out inspection with special means. Therefore, if the laser light source has run down so that its malfunction in lighting causes the use of it impossible, is difficult to easily judge the life termination factor.
In order to perform the life control of a laser light source with high reliability, it is desirable to control the lighting period of time of the laser light source. However, the laser light source, which is subjected to an intermittent lighting on/off control by controlling its lighting condition under a program control in various modes or by lighting only at its use time, has not been subjected to a lighting time control. In order to determine the lighting time of the laser light source, it is considered that the laser light source is continuously used from the use starting time. However, this method causes a shortened operational life of the laser light source and a periodical exchange of the laser light source, thus boosting the manufacturing cost.